Phreatogammarus fragilis is an endemic New Zealand crustacean that lives in aquifers. It is an amphipod (a relative of the sand hopper), and is one of the largest (commonly up to 25 mm excl. antennae) and strongest swimming of NZ’s stygofaunal* crustaceans. Because it is so rarely observed, it does not have a common name; the best translations are ‘fragile well shrimp’ or ‘fragile groundwater lobster’, ‘fragile’ probably because its appendages broke off when early specimens were being identified and preserved.

The individual below is a 12 mm-long female with a brood pouch beneath the abdomen. It is white and translucent because there is no point in investing in pigments if it’s too dark to see or if there’s no risk of sunburn. This individual was caught in a trap in a 6 m-deep well beside the Selwyn River in Canterbury by Nelson Bousted and identified by Graham Fenwick. It was photographed live in water in a custom-built aquarium with several off-camera flashes.

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Photo credit: Nelson Boustead

Waiology will have some more in-depth science of stygofauna in a future post.

* Stygofauna: animals that live in groundwaters, named after the river in Greek mythology, the Styx, which separated the Earth from the Underworld.

Dr Daniel Collins is a hydrologist and water resources scientist at NIWA.